1. Field of the Invention
The present invention generally relates to a hybrid processing method and apparatus. In the hybrid processing method, a self-contained or built-in positioning method using a vehicle speed sensor, a gyro sensor or the like, is combined with a GPS (Global Positioning System) method of positioning or measuring a current position of a movable body on the basis of radio waves from GPS satellites. Similarly, in the hybrid processing apparatus, a self-contained or built-in positioning apparatus using a vehicle speed sensor, a gyro sensor or the like, is combined with a GPS apparatus. The present invention also relates to a navigation system including the above-mentioned hybrid processing apparatus, a program storage device and a computer data signal embodiment in a carrier wave, which allow a computer to function as the hybrid processing apparatus.
2. Description of the Related Art
Nowadays a navigation system of a movable body such as a vehicle, an airplane, a ship or the like generally performs various types of hybrid processing, in which the self-contained positioning measurement using a vehicle speed sensor, a gyro sensor or the like, is combined with the GPS measurement in one way or another.
For example, Japanese Patent Application Laying Open NO. Hei 10-307036 discloses such a technique that an error correction is performed with respect to acceleration data, drive distance data, advance azimuth data or the like as self-contained positioning data, on the basis of GPS measurement.
Moreover, as for the GPS measurement, a current position is calculated independently, for example, every one or two seconds. Thus, there is such a technique to estimate or predict the current position, which is to be calculated next time i.e., for the n+1-th time, by virtue of a Kalman filter, a position filter or the like with using the current position calculated this time i.e., for the n-th time as a standard, and to thereby perform an error correction based on this estimated or predicted position with respect to the current position, which is actually calculated for the n+1-th time. Accordingly, the corrected current position can be calculated with a higher accuracy.
By the way, the radio wave from the GPS satellite may have other paths to go through to the GPS receiver after reflecting on the surface of a huge building or the like once or more times, in addition to the path to go direct to the GPS receiver, especially around the huge building such as a skyscraper, a high-rise building, or the like. This phenomenon, under which the radio waves are received at the same time through a plurality of radio wave paths from the one identical GPS satellite, is called as a xe2x80x9cmulti-pathxe2x80x9d. When the multi-path in this kind is generated, the accuracy of the GPS measurement deteriorates. Namely, the GPS measurement has such a disadvantage that the generation of the multi-path certainly deteriorates a positioning accuracy.
On the other hand, as for a self-contained sensor such as a gyro sensor or the like as described above, it has a big start drift when switching on a power. Then, if, for example, the start drift of a gyro sensor occurs, an angle is calculated with deviation. Therefore, a specification of a gyro sensor or the like describes that the error of its output increases for a predetermined period such as 10 min or 15 min after starting. Consequently, there is concern that the accuracy of the GPS measurement deteriorates more if the output of the self-contained sensor is reflected to the GPS measurement within this predetermined period after starting.
However, there is such a problem that, if the accuracy of the GPS measurement deteriorates by the generation of the multi-path as described above for 10 min or 15 min after starting, the positioning accuracy by the hybrid based on the GPS measurement data deteriorates similarly.
It is therefore an object of the present invention to provide a hybrid processing method and apparatus, which can measure a position with a relatively high accuracy after starting including just after starting a navigation system, an on-vehicle navigation system including the above-mentioned hybrid processing apparatus, as well as a program storage device and a computer data signal embodiment in a carrier wave, which allow a computer to function as the hybrid processing apparatus.
The above object of the present invention can be achieved by a hybrid processing method of outputting current position data, which indicate a current position of a movable body on which a self-contained positioning device and a GPS device are mounted, on the basis of self-contained positioning data from the self-contained positioning device and GPS measurement data from the GPS device, the method provided with: a judgment process of judging whether or not an estimated error of the self-contained positioning data is greater than a predetermined threshold value; a first calculation process of calculating the current position by combining the GPS measurement data with the self-contained positioning data if the estimated error is judged not greater than the predetermined threshold value; a second calculation process of calculating the current position from the GPS measurement data without combining the GPS measurement data with the self-contained positioning data if the estimated error is judged greater than the predetermined threshold value; and an output process of outputting the current position calculated by the first or second calculation process as the current position data which indicate the current position of the movable body.
According to the hybrid processing method of the present invention, such a judgment is performed by a judgment process that whether or not an estimated or predicted error of the self-contained positioning data is greater than a predetermined threshold value. This kind of estimated or predicted error may be calculated by the self-contained positioning device and may be outputted together with the self-contained positioning data. Alternatively, it may be calculated on the basis of the self-contained positioning data outputted from the self-contained positioning device. The predetermined threshold value is individually and concretely determined depending on the each specification of the self-contained positioning devices or the like experientially, experimentally, theoretically, or simulationally etc. It may be a fixed value or a variable value depending on an actual operational condition. Then, the current position is calculated by the first calculation process by combining the GPS measurement data with the self-contained positioning data if the estimated error is judged not greater than the predetermined threshold value. Namely, if the estimated error is to some degree small even after starting the navigation system, including just after starting the navigation system, the start drift of the self-contained positioning data is relatively minor. Accordingly, when combining the self-contained positioning data with the GPS measurement data, the action or effect of restraining the accuracy deterioration due to the multi-path etc., in the GPS measurement data by virtue of the self-contained positioning data becomes superior to the action or effect of deteriorating the measurement accuracy due to the start drift. Therefore, in this case, it can effectively prevent the accuracy of such a finally outputted current position from being degraded due to the deterioration of the GPS measurement accuracy by the multi-path or the like by calculating the corrected current position as combining the GPS measurement data with the self-contained positioning data in the first calculation process.
On the other hand, the current position is calculated by the second calculation process by the GPS measurement data without combining the GPS measurement data with the self-contained positioning data if the estimated error is judged greater than the predetermined threshold value. Namely, if the estimated error is to some degree considerable after starting the navigation system, including just after starting the navigation system, the start drift of the self-contained positioning data is considered relatively large. Accordingly, when combining the self-contained positioning data with the GPS measurement data, the action or effect of deteriorating the measurement accuracy due to the start drift becomes superior to the action or effect of restraining the accuracy deterioration due to the multi-path etc., in the GPS measurement data by virtue of the self-contained positioning data. Therefore, in this case, it can effectively prevent the accuracy of such a finally outputted current position from being degraded due to the deterioration of the self-contained positioning accuracy by the start drift, by calculating the current position only from the GPS measurement data in the second calculation process.
As a result, it is possible to measure or position with a relatively high accuracy by the hybrid processing even after starting the navigation system, including just after starting the navigation system.
In one aspect of the hybrid processing method, estimated error data, which indicate the estimated error, are outputted from the self-contained positioning device and the judgment process performs the judgment on the basis of the estimated error data.
According to this aspect, the estimated error data are outputted from the self-contained positioning device in real time. This is done by the similar or the same software processing or the like as that of a built-in microcomputer of a gyro sensor for outputting the estimated error data, which are traditionally used for decision of an object range of map matching or for a standard of how urgent an error correction to the self-contained positioning measurement result is, for example. Consequently, the judgment based on the estimated error data in the judgment process can be relatively easily performed on the basis of the estimated error data outputted in real time from the self-contained positioning device.
Alternatively, in another aspect of the hybrid processing method, the method is further provided with an estimated error calculation process of calculating the estimated error on the basis of the self-contained positioning data.
According to this aspect, even if the self-contained positioning device is not provided with a function of outputting the estimated error data, it is possible to calculate the estimated error on the basis of the self-contained positioning data or the like from the self-contained positioning device, by the estimated error calculation process. If using the estimated error as calculated above, it is possible to perform the judgment in the judgment process relatively easily and surely.
In another aspect of the hybrid processing method, the first calculation process (i) calculates the n-th measurement position from the GPS measurement data outputted for the n-th time (n is a natural number) by the GPS device, (ii) estimates the n+1-th measurement position as an estimated position depending on the self-contained positioning data with using the n-th measurement position as a standard, (iii) calculates the n+1-th measurement position from the GPS measurement data outputted for the n+1-th time by the GPS device, and (iv) performs an error correction based on the estimated position with respect to the n+1-th measurement position, to thereby calculate the n+1-th corrected measurement position as the current position, and the second calculation process (v) calculates the n-th measurement position from the GPS measurement data outputted for the n-th time by the GPS device, (vi) estimates the n+1-th measurement position as an estimated position depending on the GPS measurement data with using the n-th measurement position as a standard, (vii) calculates the n+1-th measurement position from the GPS measurement data outputted for the n+1-th time by the GPS device, and (viii) performs an error correction based on the estimated position with respect to the n+1-th measurement position, to thereby calculate the n+1-th corrected measurement position as the current position.
According to this aspect, the n-th measurement position is calculated from the GPS measurement data outputted for the n-th time (i.e. previous time) in the first calculation process, if the estimated error is judged not greater than the predetermined threshold value by the judgment process. Then, the n+1-th measurement position is estimated as an estimated position depending on the self-contained positioning data such as a vehicle speed sensor, a gyro sensor, or the like with using the n-th measurement position as a standard. This estimation is performed by using a position filter, a Kalman filter, or the like, which are well known to the art. Then, the n+1-th measurement position is calculated from the GPS measurement data outputted for the n+1-th time (i.e. current time) by the GPS device. Moreover an error correction based on the estimated position estimated by using the above-mentioned Kalman filter or the like is performed with respect to the n+1-th measurement position and the n+1-th corrected measurement position is calculated as the current position.
On the other hand, if the estimated error is judged greater than the predetermined threshold value by the judgment process, the n-th measurement position is calculated from the GPS measurement data outputted for the n-th time (i.e. previous time) in the second calculation process. Then, the n+1-th measurement position is estimated as an estimated position depending on the GPS measurement data (e.g. the GPS measurement data which are outputted for the n-th time, for the nxe2x88x921-th time, for the nxe2x88x922-th time, . . . , and which are stored in a memory or the like) with using the n-th measurement position as a standard. This estimation is performed by a Kalman filter which is well known to the art. Then, the n+1-th measurement position is calculated from the GPS measurement data outputted for the n+1-th time (i.e. current time). Moreover, an error correction based on the estimated position estimated by using the above-mentioned Kalman filter or the like is performed with respect to the n+1-th measurement position, and the n+1-th corrected measurement position is calculated as the current position.
Consequently, according to this aspect, it is possible to measure or position with a relatively high accuracy by the hybrid processing, by using the GPS measurement data in estimating the estimated position if the estimated error of the self-contained positioning data is relatively large while by using the self-contained positioning data in estimating the estimated position if the estimated error of the self-contained positioning data is relatively small.
In another aspect of the hybrid processing, the judgment process performs the judgment before elapsing a predetermined period from a time of switching on a power of the self-contained positioning device and does not perform the judgment after elapsing the predetermined period, and if the judgment is not performed, the present position is calculated by the first calculation process.
According to this aspect, the judgment by the judgment process is performed if it is before elapsing a predetermined period from a time of switching on a power of the self-contained positioning device. Namely, the judgment process is performed under the condition that the error by the start drift may be more or less generated. The judgment by the judgment process is not performed if it is after elapsing the predetermined period, and the current position is calculated by the first calculation process. Namely, the judgment process is not performed under the condition that the error by the start drift is not generated, and the current position is calculated by combining the self-contained positioning data with the GPS measurement data by the first calculation process.
The above object of the present invention can be achieved by a hybrid processing apparatus for outputting current position data, which indicate a current position of a movable body on which a self-contained positioning device and a GPS device are mounted, on the basis of self-contained positioning data from the self-contained positioning device and GPS measurement data from the GPS device, the apparatus provided with: a judgment device for judging whether or not an estimated error of the self-contained positioning data is greater than a predetermined threshold value; a first calculation device for calculating the current position by combining the GPS measurement data with the self-contained positioning data if the estimated error is judged not greater than the predetermined threshold value; a second calculation device for calculating the current position from the GPS measurement data without combining the GPS measurement data with the self-contained positioning data if the estimated error is judged greater than the predetermined threshold value; and an output device for outputting the current position calculated in the first or second calculation device as the current position data which indicate the current position of the movable body.
According to the hybrid processing apparatus of the present invention, such a judgment is performed by a judgment device.that whether or not an estimated error of the self-contained positioning data is greater than a predetermined threshold value. Then, the current position is calculated by the first calculation device by combining the GPS measurement data with the self-contained positioning data if the estimated error is judged not greater than the predetermined threshold value. Namely, in this case, it can effectively prevent the accuracy of such a finally outputted current position from being degraded due to the deterioration of the GPS measurement accuracy by the multi-path or the like, by calculating the correct current position while combining the GPS measurement data with the self-contained positioning data in the first calculation device.
On the other hand, the current position is calculated by the second calculation device by the GPS measurement data without combining the GPS measurement data with the self-contained positioning data if the estimated error is judged greater than the predetermined threshold value. Namely, in this case, it can effectively prevent the accuracy of such a finally outputted current position from being degraded due to the deterioration of the accuracy of the self-contained positioning measurement by the multi-path or the like, by calculating the correct current position only from the GPS measurement data in the second calculation device.
As a result, it is possible to measure or position with a relatively high accuracy by the hybrid processing even after starting the navigation system, including just after starting the navigation system.
In one aspect of the hybrid processing apparatus, estimated error data, which indicate the estimated error, are outputted from the self-contained positioning device and the judgment device performs the judgment on the basis of the estimated error data.
According to this aspect, the estimated error data are outputted from the self-contained positioning device in real time by the similar or the same software processing or the like as that of a built-in microcomputer of a gyro sensor, for example. Consequently, the judgment based on the estimated error data in the judgment process can be relatively easily performed.
Alternatively, in another aspect of the hybrid processing apparatus, the apparatus is further provided with an estimated error calculation device for calculating the estimated error on the basis of the self-contained positioning data.
According to this aspect, even if the self-contained positioning device is not provided with a function of outputting the estimated error data, it is possible to calculate the estimated error on the basis of the self-contained positioning data or the like from the self-contained positioning device by the estimated error calculation device. If using the estimated error as calculated above, it is possible to perform the judgment in the judgment device relatively easily and surely.
In another aspect of the hybrid processing apparatus, the first calculation device (i) calculates the n-th measurement position from the GPS measurement data outputted for the n-th time (n is a natural number) by the GPS device, (ii) estimates the n+1-th measurement position as an estimated position depending on the self-contained positioning data with using the n-th measurement position as a standard, (iii) calculates the n+1-th measurement position from the GPS measurement data outputted for the n+1-th time by the GPS device, and (iv) performs an error correction based on the estimated position with respect to the n+1-th measurement position, to thereby calculate the n+1-th corrected measurement position as the current position, and the second calculation device (v) calculates the n-th measurement position from the GPS measurement data outputted for the n-th time by the GPS device, (vi) estimates the n+1-th measurement position as an estimated position depending on the GPS measurement data with using the n-th measurement position as a standard, (vii) calculates the n+1-th measurement position from the GPS measurement data outputted for the n+1-th time by the GPS device, and (viii) performs an error correction based on the estimated position with respect to the n+1-th measurement position, to thereby calculate the n+1-th corrected measurement position as the current position.
According to this aspect, the n-th measurement position is calculated from the GPS measurement data outputted for the n-th time (i.e. previous time) in the first calculation device, if the estimated error is judged not greater than the predetermined threshold value by the judgment device. Then, the n+1-th measurement position is estimated as an estimated position depending on the self-contained positioning data such as a vehicle speed sensor, a gyro sensor, or the like with the n-th measurement position as a standard. Then, the n+1-th measurement position is calculated from the GPS measurement data outputted for the n+1-th time (i.e. current time) by the GPS device. Moreover an error correction based on the estimated position is performed with respect to the n+1-th measurement position, and the n+1-th corrected measurement position is calculated as the current position.
On the other hand, if the estimated error is judged greater than the predetermined threshold value by the judgment process, the n-th measurement position is calculated from the GPS measurement data outputted for the n-th time (i.e. previous time) in the second calculation process. Then, the n+1-th measurement position is estimated as an estimated position depending on the GPS measurement data with using the n-th measurement position as a standard. Then, the n+1-th measurement position is calculated from the GPS measurement data outputted for the n+1-th time (i.e. current time). Moreover, an error correction based on the estimated position is performed with respect to the n+1-th measurement position, and the n+1-th corrected measurement position is calculated as the current position.
Consequently, according to this aspect, it is possible to measure or position with a relatively high accuracy by the hybrid processing, by using the GPS measurement data in estimating the estimated position if the estimated error of the self-contained positioning data is relatively large while by using the self-contained positioning data in estimating the estimated position if the estimated error of the self-contained positioning data is relatively small.
In another aspect of the hybrid processing apparatus, the judgment device performs the judgment before elapsing a predetermined period from a time of switching on a power of the self-contained positioning device and does not perform the judgment after elapsing the predetermined period, and if the judgment is not performed, the present position is calculated by the first calculation device.
According to this aspect, the judgment by the judgment device is performed if it is before elapsing a predetermined period from a time of switching on a power of the self-contained positioning device. Namely, the judgment device is performed under the condition that the error by the start drift may be more or less generated. The judgment by the judgment device is not performed if it is after elapsing the predetermined period, and the current position is calculated by the first calculation device. Namely, the judgment device is not performed under the condition that the error by the start drift is not generated, and the current position is calculated by combining the self-contained positioning data with the GPS measurement data by the first calculation device.
The above object of the present invention can be achieved by an on-vehicle navigation system provided with: the above-mentioned hybrid processing apparatus of the present invention (including its various aspects), the self-contained positioning device and the GPS device, and a display device for displaying the current position data outputted from the output device on map data in a predetermined format.
According to this aspect of the on-vehicle navigation system of the present invention, the self-contained positioning data are outputted from the self-contained positioning device and the GPS measurement data are outputted from the GPS device. Then, these data are appropriately combined depending on how considerable the estimated error of the self-contained positioning data is by the above-mentioned hybrid processing apparatus of the present invention and the current position data are outputted. Then, the current position data are displayed on map data in a predetermined format by the display device. Therefore, it is possible to display the highly accurate current position data on a map even after starting the navigation system, including just after starting the navigation system.
The above object of the present invention can be also achieved by a program storage device readable by a computer. The program storage device stores a program of instructions to cause the computer to function as at least one portion of the above-described hybrid processing apparatus of the present invention (including its various aspects).
According to the program storage device, such as a CD-ROM, a ROM, a DVD, a floppy disk or the like, of the present invention, the above described hybrid processing apparatus of the present invention can be relatively easily realized as a computer reads and executes the program of instructions or as it executes the program after downloading the program through communication device. Moreover, the program of instructions can be sent from a central device with an application program required for the navigation or other data such as a map.
The above object of the present invention can be also achieved by a computer data signal embodied in a carrier wave and representing a series of instructions for a computer. The series of instructions causes the computer to function as at least one portion of the above-described hybrid processing apparatus of the present invention (including its various aspects).
According to this computer data signal embodied in the carrier wave of the present invention, as the computer downloads the program in the computer data signal through a computer network or the like, and executes this program, it is possible to realize the above described hybrid processing apparatus of the present invention.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with reference to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.